1. Field of the Invention
The present invention relates to an image resolution conversion apparatus and, more particularly, the present invention relates to an image resolution conversion apparatus, preferable for converting the resolution of an original image having pixel values by an arbitrary magnification ratio, for generating new pixel values in newly set pixel positions.
2. Description of the Related Art
A conventional technique for converting the resolution of an image is disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. 2001-238073. The conventional technique will be explained with reference to FIG. 18. According to the method proposed in the publication, a new-pixel-generating region is surrounded by the original 2 lines by 2 columns of image pixels forming a rectangle; and a group of 4 lines by 4 columns of sixteen pixels of original image, including these four pixels and surrounding pixels in neighboring lines and columns are used for calculating the newly generated pixel. The pixel values of the newly generated pixels are calculated based on the pixel values of the 4 lines by 4 columns of sixteen pixels by a cubic interpolation process, etc.
Although converting the resolution of an interlaced image per frame unit is advantageous from an image quality point of view, this method is subject to more than one field of delay. From a real time process point of view, processing per field unit is more desirable where no delay is allowed.
The method proposed by Japanese Unexamined Patent Application, First Publication No. 2001-238073 uses a pixel group including 4 lines by 4 columns of sixteen pixels in the original image for generating a new pixel. However, using this method for processing the interlaced image per unit field causes the following significant change in the distribution range of a pixel group with respect to a line direction and a column direction.
FIG. 19 illustrates how it changes. Round spots indicate pixel positions of an original image viewed in a field unit of an interlaced image. Cross points of grid lines indicate pixel positions of the original image obtained by viewing two integrated fields. An interval of columns corresponds to one pixel and an interval of lines corresponds to two pixels since data do not exist in every one line when viewing two interlaced images per field unit. That is, the range of unit field including 4 lines by 4 columns corresponds to a frame including integrated fields consisting of 7 lines by 4 columns.